This invention relates to a dispersing agent for nonaqueous systems and a nonaqueous dispersion containing the dispersing agent. More particularly, this invention relates to a dispersing agent which is conducive to the production of dispersions of finely divided solid powders in nonaqueous media with improved dispersibility and dispersion stability and nonaqueous dispersions prepared with the aid of the dispersing agent.
As dispersing agents for use in dispersing finely divided solids in nonaqueous solvents, polyesters of 12-hydroxystearic acid and polyesters of castor oil fatty acid (acid values ranging from 10 to 100 mg-KOH/g), for instance, have been proposed in Japanese Patent Publication No. 54-34009. Lanolin-based surfactants have also been described in Vinyl and Polymers 20, (1), 12-20 (1980) (Institute of Polymer Industry). Moreover, Japanese Patent Publication No. 56-45515 suggests the use of lanolin fatty acid soap as a dispersing agent for pigments.
However, these known dispersing agents cannot provide a nonaqueous dispersion with sufficient dispersibility and dispersion stability and if only for the reason that, on prolonged storage, solid particles separate out from the dispersion, have not proved satisfactory in field performance.
Meanwhile, efforts have been being made to provide lubricating oils such as mineral, synthetic, animal, vegetable and other oil with sufficient resistance to super-high pressure and friction by incorporating various solid or liquid additives and its is known to be particularly beneficial to add a solid lubricating agent such as carbon fluoride powder or fluororesin powder to the base lubricating oil.
However, carbon fluoride and fluororesin are so low in the affinity for oils in general that such lubricating oil systems are extremely unstable, undergoing flocculation and settling within one day after addition of the powder. Therefore, as dispersing agents for use in dispersing solid lubricants, Japanese Patent KOKAI Publication No. 60-56760 recommends nonionic surfactants such as polyoxypropylene alkyl ethers, polyoxypropylene alkyl phenyl ethers and so on.
However, dispersions obtained with these known dispersing agents for solid lubricants are not sufficiently stable and fail to exhibit the desired lubricating function under field conditions. Moreover, these dispersing agents form sediments on prolonged standing. Therefore, such dispersions cannot be satisfactory lubricating oil systems.